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In order to clarify the pore structure characteristics of deep coking coal in Pingdingshan No.12 Coal Mine, low-temperature nitrogen adsorption method and mercury intrusion method were used to conduct experimental research on its soft and hard coal. The pore structure fractal was carried out on the parameters measured by mercury intrusion method using the Menger sponge model. The results show that the low-temperature nitrogen adsorption isotherms of soft and hard coal in Pingdingshan coking coal are close to the IV isotherm, the development of soft and hard coal is relatively consistent, and there is a small hysteresis loop. The types of micropore and small pore are mainly the impermeable pore and closed pore with one end closed, and the pores above the middle pore are mainly open and permeable; the pore area of soft coal measured by mercury intrusion method is 5.058 m2/g, the pore volume is 0.037 5 cm3/g, the pore area of hard coal is 4.641 m2/g, and the pore volume is 0.036 8 cm3/g. The pore size distribution of soft and hard coal is relatively consistent, the adsorption space is concentrated in micropores and small pores, and a higher proportion of micropores is conducive to gas storage; the pore characteristics of coking coal samples show a “polarization” distribution, and the macropores, visible pores and cracks are compared. It is conducive to the flow and drainage of coal seam gas in Pingdingshan No.12 Coal Mine, but a small proportion of mesoporous pores may result in poor gas production and migration channels; soft and hard coal seepage pores have obvious fractal characteristics, the fractal dimension of adsorption pores is generally higher than that of seepage pores, indicating that the pore structure of micro-pores is more complex and irregular.

In order to study the change of pore structure and adsorption characteristics of coking coal after the high-temperature and high-pressure adsorption test, the coking coal from the Liulin coalmine was selected for the research. Both the mercury injection experiments were carried out on the raw coal and the coal after the isothermal adsorption experiment processing with a pressure of 11 MPa and temperature ranging from 30 to 90°C. The results show that the pressure is beneficial to gas adsorption, while the temperature has a restraining effect on the gas adsorption of coking coal, and there is a good negative exponential relationship between the adsorption capacity and temperature. The hysteresis loop of that after the high-temperature and high-pressure isothermal adsorption test is smaller than that of raw coal, and the connectivity of pores becomes worse. In the process of the mercury injection experiment, the hysteresis loop of coking coal after the high-temperature and high-pressure adsorption experiment is smaller than that of raw coal. This demonstrates that the open pores decrease and the semi-closed pores increase, and then the connectivity of the pores becomes worse, which is not conducive to the gas flow when the coking is subjected to high-temperature and high-pressure action. After the high-temperature and high-pressure adsorption experiment, the volume of macropores, visible pores, and crannies of the coking coal decreases, and the volume of micropores and minipores increases. However, the total pore volume reduced overall. Under the same pressure, with the increase in temperature, the volume of macropores, visible pores, and crannies increases, while the volume of micropores and minipores decreases, and the total pore volume increases. After the high-temperature and high-pressure adsorption experiment, the proportion of micropores and minipores increases, and the specific surface area also increases. Under the same pressure, the surface areas of micropores and minipores decrease and the total specific surface area also decreases with the increase in temperature.